Characterization of new medium-chain alcohol dehydrogenases adds resolution to duplications of the class I/III and the sub-class I genes

► Functional and structural characterization of the major dogfish liver alcohol dehydrogenase (ADH) showed it to be of class III type, which establishes a refinement in time of divergence for the ADH class III/I genes. ► The similar analysis of the major feral pigeon liver ADH showed it to be of class I type, which via phylogenetic tree calculations give estimates for the time of an ADH sub-class I gene duplication. ► The latter analysis also contributes to refinements in the early and successive origins of the avian orders.